As the devices forming integrated circuits have become smaller, the topography of semiconductor slices during intermediate stages of fabrication has worsened. This in turn has led to problems in patterning integrated circuit workpiece surfaces with extreme topography by means of a single photoresist layer.
To meet this problem, bilayer and trilayer photoresist systems have been developed. D. Hoffer et al. ("Advances in Resist Technology" SPIE, Vol. 469 (1984)) report a silicon-based polymer as a deep-ultraviolet, positive resist. They also report that silicon-based resists can act as excellent reactive ion etch (RIE) barriers in an oxygen plasma. They used a mid-ultraviolet (313 nm) projection tool to expose the resist.
Workers in the art have reported trilayer processes that use a two-stage etch process to pattern a bottom layer. However, these trilayer processes use a middle layer that is plasma-deposited and that is usually inorganic in nature. Standard multi-layer photographic techniques have problems in throughput rate, complication of processing, uniformity control, cleanliness, layer cracking and removal of the deposited layers. A need has therefore arisen for a trilayer photolithograhic process that has improved throughput and quality control characteristics as opposed to conventional trilayer processes.